Configuration reference

This page explains the variables found in mailu.env. In most cases mailu.env is setup correctly by the setup utility and can be left as-is. However, some advanced settings or modifications can be done by modifying this file.

Common configuration

The SECRET_KEY must be changed for every setup and set to a 16 bytes randomly generated value. It is intended to secure authentication cookies among other critical uses. This can be generated with a utility such as pwgen, which can be installed on most Linux systems:

apt-get install pwgen
pwgen 16 1

The DOMAIN holds the main e-mail domain for the server. This email domain is used for bounce emails, for generating the postmaster email and other technical addresses.

The HOSTNAMES are all public hostnames for the mail server. Mailu supports a mail server with multiple hostnames. The first declared hostname is the main hostname and will be exposed over SMTP, IMAP, etc.

The SUBNET defines the address range of the docker network used by Mailu. This should not conflict with any networks to which your system is connected. (Internal and external!). Normally this does not need to be changed, unless there is a conflict with existing networks.

The POSTMASTER is the local part of the postmaster email address. It is recommended to setup a generic value and later configure a mail alias for that address.

The WILDCARD_SENDERS setting is a comma delimited list of user email addresses that are allowed to send emails from any existing address (spoofing the sender).

The AUTH_RATELIMIT_IP (default: 5/hour) holds a security setting for fighting attackers that attempt a password spraying attack. The value defines the limit of authentication attempts that will be processed on distinct non-existing accounts for a specific IP subnet as defined in AUTH_RATELIMIT_IP_V4_MASK (default: /24) and AUTH_RATELIMIT_IP_V6_MASK (default: /48).

The AUTH_RATELIMIT_USER (default: 50/day) holds a security setting for fighting attackers that attempt to guess a user’s password (typically using a password brute-force attack). The value defines the limit of distinct authentication attempts allowed for any given account within a specific time-frame. Multiple attempts for the same account with the same password only counts for one.

The AUTH_RATELIMIT_EXEMPTION_LENGTH (default: 86400) is the number of seconds after a successful login for which a specific IP address is exempted from rate limits. This ensures that users behind a NAT don’t get locked out when a single client is misconfigured… but also potentially allow for users to attack each-other.

The AUTH_RATELIMIT_EXEMPTION (default: ‘’) is a comma separated list of network CIDRs that won’t be subject to any form of rate limiting. Specifying, ::/0 there is a good way to disable rate limiting altogether.

The TLS_FLAVOR sets how Mailu obtains a x509 certificate. More on TLS certificates.

The DEFAULT_SPAM_THRESHOLD (default: 80) is the default spam tolerance used when creating a new user.

Mail settings

The MESSAGE_SIZE_LIMIT is the maximum size of a single email. It should not be too low to avoid dropping legitimate emails and should not be too high to avoid filling the disks with large junk emails.

The MESSAGE_RATELIMIT (default: 200/day) is the maximum number of messages a single user can send. MESSAGE_RATELIMIT_EXEMPTION contains a comma delimited list of user email addresses that are exempted from any restriction. Those settings are meant to reduce outbound spam in case of compromised or malicious account on the server.

The RELAYNETS (default: unset) is a comma delimited list of network addresses for which mail is relayed for with no authentication required. This should be used with great care as misconfigurations may turn your Mailu instance into an open-relay!

The RELAYHOST is an optional address to use as a smarthost for all outgoing mail in following format: [HOST]:PORT. RELAYUSER and RELAYPASSWORD can be used when authentication is required.

By default postfix uses “opportunistic TLS” for outbound mail. This can be changed by setting OUTBOUND_TLS_LEVEL to encrypt or secure. This setting is highly recommended if you are using a relayhost that supports TLS but discouraged otherwise. DEFER_ON_TLS_ERROR (default: True) controls whether incomplete policies (DANE without DNSSEC or “testing” MTA-STS policies) will be taken into account and whether emails will be deferred if the additional checks enforced by those policies fail.

Similarly by default nginx uses “opportunistic TLS” for inbound mail. This can be changed by setting INBOUND_TLS_ENFORCE to True. Please note that this is forbidden for internet facing hosts according to e.g. RFC 3207 , because this prevents MTAs without STARTTLS support or e.g. mismatching TLS versions to deliver emails to Mailu.

The SCAN_MACROS (default: True) setting controls whether Mailu will endeavor to reject emails containing documents with malicious macros. Under the hood, it uses mraptor from oletools to determine whether a macro is malicious or not.

When FETCHMAIL_ENABLED is set to True, the fetchmail functionality is enabled and shown in the admin interface. The container itself still needs to be deployed manually. FETCHMAIL_ENABLED defaults to True.

The FETCHMAIL_DELAY is a delay (in seconds) for the fetchmail service to go and fetch new email if available. Do not use too short delays if you do not want to be blacklisted by external services, but not too long delays if you want to receive your email in time.

The RECIPIENT_DELIMITER is a list of characters used to delimit localpart from a custom address part. For instance, if set to +-, users can use addresses like or to deliver mail to This is useful to provide external parties with different email addresses and later classify incoming mail based on the custom part.

The DMARC_RUA and DMARC_RUF are DMARC protocol specific values. They hold the localpart for DMARC rua and ruf email addresses.

The FULL_TEXT_SEARCH variable (default: ‘en’) is a comma separated list of language codes as defined on fts_languages. This feature can be disabled (e.g. for performance reasons) by setting the variable to off.

You can set a global DEFAULT_QUOTA to be used for mailboxes when the domain has no specific quota configured.

Web settings

  • WEB_ADMIN contains the path to the main admin interface

  • WEB_WEBMAIL contains the path to the Web email client.

  • WEB_API contains the path to the RESTful API.

  • WEBROOT_REDIRECT redirects all non-found queries to the set path. An empty WEBROOT_REDIRECT value disables redirecting and enables classic behavior of a 404 result when not found. Alternatively, WEBROOT_REDIRECT can be set to none if you are using an Nginx override for location /.

All four options need a leading slash (/) to work.


WEBROOT_REDIRECT has to point to a valid path on the webserver. This means it cannot point to any services which are not enabled. For example, don’t point it to /webmail when WEBMAIL=none

Both SITENAME and WEBSITE are customization options for the panel menu in the admin interface, while SITENAME is a customization option for every Web interface.

  • LOGO_BACKGROUND sets a custom background colour for the brand logo in the top-left of the main admin interface. For a list of colour codes refer to this page of w3schools.

  • LOGO_URL sets a URL for a custom logo. This logo replaces the Mailu logo in the top-left of the main admin interface.

Admin account - automatic creation

For administrative tasks, an admin user account will be needed. You can create it manually, after deploying the system, or automatically. To create it manually, follow the specific deployment method documentation.

To have the account created automatically, you just need to define a few environment variables:

  • INITIAL_ADMIN_ACCOUNT: the admin username: The first part of the e-mail address before the @.

  • INITIAL_ADMIN_DOMAIN: the domain appendix: Most probably identical to the DOMAIN variable.

  • INITIAL_ADMIN_PW: the admin password.

  • INITIAL_ADMIN_MODE: use one of the options below for configuring how the admin account must be created:

    • create: (default) creates a new admin account and raises an exception when it already exists.

    • ifmissing: creates a new admin account when the admin account does not exist.

    • update: creates a new admin account when it does not exist, or update the password of an existing admin account.

Note: It is recommended to set INITIAL_ADMIN_MODE to either update or ifmissing. Leaving it with the default value will cause an error when the system is restarted.

An example:


Depending on your particular deployment you most probably will want to change the default.

Advanced settings

The AUTH_REQUIRE_TOKENS (default: False) setting controls whether thick clients can authenticate using passwords or whether they are forced to use tokens/application specific passwords.

The API_TOKEN (default: None) setting configures the authentication token. The minimum length is 3 characters. This token must be passed as request header to the API as authentication token. This is a mandatory setting for using the RESTful API.

The CREDENTIAL_ROUNDS (default: 12) setting is the number of rounds used by the password hashing scheme. The number of rounds can be reduced in case faster authentication is needed or increased when additional protection is desired. Keep in mind that this is a mitigation against offline attacks on password hashes, aiming to prevent credential stuffing (due to password re-use) on other systems.

The SESSION_COOKIE_SECURE (default: True) setting controls the secure flag on the cookies of the administrative interface. It should only be turned off if you intend to access it over plain HTTP.

SESSION_TIMEOUT (default: 3600) is the maximum amount of time in seconds between requests before a session is invalidated. PERMANENT_SESSION_LIFETIME (default: 108000) is the maximum amount of time in seconds a session can be kept alive for if it hasn’t timed-out.

The LOG_LEVEL setting is used by the python start-up scripts as a logging threshold. Log messages equal or higher than this priority will be printed. Can be one of: CRITICAL, ERROR, WARNING, INFO, DEBUG or NOTSET. See the python docs for more information.

The LETSENCRYPT_SHORTCHAIN (default: False) setting controls whether we send the ISRG Root X1 certificate in TLS handshakes. This is required for android handsets older than 7.1.1 but slows down the performance of modern devices.

The TLS_PERMISSIVE (default: true) setting controls whether ciphers and protocols offered on port 25 for STARTTLS are optimized for maximum compatibility. We strongly recommend that you do not change this setting on the basis that any encryption beats no encryption. If you are subject to compliance requirements and are not afraid of losing emails as a result of artificially reducing compatibility, set it to ‘false’. Keep in mind that servers that are running a software stack old enough to not be compatible with the current TLS requirements will either a) deliver in plaintext b) bounce emails c) silently drop emails; moreover, modern servers will benefit from various downgrade protections (DOWNGRD, RFC7507) making the security argument mostly a moot point.

The COMPRESSION (default: unset) setting controls whether emails are stored compressed at rest on disk. Valid values are gz, bz2 or zstd and additional settings can be configured via COMPRESSION_LEVEL, see zlib_save_level for accepted values. If the underlying filesystem supports compression natively you should use it instead of this setting as it will be more efficient and will improve compatibility with 3rd party tools.

The REAL_IP_HEADER (default: unset) and REAL_IP_FROM (default: unset) settings controls whether HTTP headers such as X-Forwarded-For or X-Real-IP should be trusted. The former should be the name of the HTTP header to extract the client IP address from and the later a comma separated list of IP addresses designating which proxies to trust. If you are using Mailu behind a reverse proxy, you should set both. Setting the former without the latter introduces a security vulnerability allowing a potential attacker to spoof their source address.

The TZ sets the timezone Mailu will use. The timezone naming convention usually uses a Region/City format. See TZ database name for a list of valid timezones This defaults to Etc/UTC. Warning: if you are observing different timestamps in your log files you should change your hosts timezone to UTC instead of changing TZ to your local timezone. Using UTC allows easy log correlation with remote MTAs.

The PORTS (default: ‘25,80,443,465,993,995,4190’) setting determines which services should be enabled. It is a comma delimited list of ports numbers. If you need to re-enable IMAP, POP3 and Submission, you can append ‘110,143,587’ to that list. Please note that ports 25,465 and 993 cannot be disabled.

The PROXY_PROTOCOL (default: unset) setting allows the the front container to receive TCP and HTTP connections with the PROXY protocol (originally introduced in HAProxy, now also configurable in other proxy servers). It can be set to a comma delimited list of ports on which it should be enabled.

This requires to have a valid REAL_IP_FROM (default: unset). Setting PROXY_PROTOCOL without setting REAL_IP_FROM will not work. The REAL_IP_HEADER must be unset. Otherwise Mailu will not accept the IP address from the remote client specified by the proxy. This results in the proxy being rate limited or even banned (when fail2ban is used). Make sure to set a REAL_IP_FROM only pointing to IP addresses or networks that you trust; accepting the PROXY protocol from untrusted sources is a serious security vulnerability, allowing a potential attacker to spoof their source address.

Antivirus settings

The ANTIVIRUS_ACTION switches behaviour if a virus is detected. It defaults to ‘discard’, so any detected virus is silently discarded. If set to ‘reject’, rspamd is configured to reject virus mails during SMTP dialogue, so the sender will receive a reject message.

Infrastructure settings

Various environment variables *_ADDRESS can be used to run Mailu containers separately from a supported orchestrator. It is used by the various components to find the location of the other containers it depends on. Those variables are:










These are used for DNS based service discovery with possibly changing services IP addresses. *_ADDRESS values must be fully qualified domain names without port numbers.

Database settings

Both the admin and roundcube services store their configurations in a SQLite database. Alternatives hosted options like PostgreSQL and MariaDB/MySQL can be configured using DB URL but the development team recommends against it. Indeed, there is currently very little data to be stored and SQLite is deemed both sufficient, simpler and more reliable overall.

  • SQLALCHEMY_DATABASE_URI (default: sqlite:////data/main.db): the SQLAlchemy database URL for accessing the database

  • SQLALCHEMY_DATABASE_URI_ROUNDCUBE (default: sqlite:////data/roundcube.db): the Roundcube database URL for accessing the Roundcube database

For PostgreSQL use driver postgresql (SQLALCHEMY_DATABASE_URI=postgresql://mailu:mailu_secret_password@database/mailu).

For MariaDB/MySQL use driver mysql+mysqlconnector (SQLALCHEMY_DATABASE_URI= mysql+mysqlconnector://mailu:mailu_secret_password@database/mailu).

For Roundcube, refer to the roundcube documentation for the URL specification.

Webmail settings

When using roundcube it is possible to select the plugins to be enabled by setting ROUNDCUBE_PLUGINS to a comma separated list of plugin-names. Included plugins are:

  • acl (needs configuration)

  • additional_message_headers (needs configuration)

  • archive

  • attachment_reminder

  • carddav

  • database_attachmentsi

  • debug_logger

  • emoticons

  • enigma

  • help

  • hide_blockquote

  • identicon

  • identity_select

  • jqueryui

  • mailu

  • managesieve

  • markasjunk

  • new_user_dialog

  • newmail_notifier

  • reconnect

  • show_additional_headers (needs configuration)

  • subscriptions_option

  • vcard_attachments

  • zipdownload

If ROUNDCUBE_PLUGINS is not set the following plugins are enabled by default:

  • archive

  • carddav

  • enigma

  • mailu

  • managesieve

  • markasjunk

  • zipdownload

To disable all plugins just set ROUNDCUBE_PLUGINS to mailu.

To configure a plugin add php files named *.inc.php to roundcube’s override section.

Header authentication using an external proxy

The PROXY_AUTH_WHITELIST (default: unset/disabled) option allows you to configure a comma separated list of CIDRs of proxies to trust for authentication. This list is separate from REAL_IP_FROM and any entry in PROXY_AUTH_WHITELIST should also appear in REAL_IP_FROM.

Use PROXY_AUTH_HEADER (default: ‘X-Auth-Email’) to customize which HTTP header the email address of the user to authenticate as should be and PROXY_AUTH_CREATE (default: False) to control whether non-existing accounts should be auto-created. Please note that Mailu doesn’t currently support creating new users for non-existing domains; you do need to create all the domains that may be used manually.

Once configured, any request to /sso/login with the correct headers will be authenticated unless the “noproxyauth” parameter is passed, in which case the “standard” login form will be displayed. Please check issues 1972 and 2692 for more details.

Requests to:

  • “/sso/login” results the user being redirected to the web administration interface after authentication.

  • “/admin” (WEB_ADMIN=/admin) results the user being redirected to the web administration interface after authentication.

  • “/webmail” (WEB_WEBMAIL=/webmail) results the user being redirected to the web administration interface after authentication.

Use PROXY_AUTH_LOGOUT_URL (default: unset) to redirect users to a specific URL after they have been logged out.